Transmitting apparatus and transmitting method

ABSTRACT

A control section  101  outputs retransmission information as to whether or not a transmit signal is a retransmission signal, and if a retransmission signal, which (first, second, etc.) retransmission this is, to a selection section  107 . An IFFT section  103  performs orthogonal frequency division multiplexing processing of the transmit signal. A GI insertion section  104  inserts a guard interval in the transmit signal. A GI insertion section  105  inserts in the transmit signal a guard interval longer than the guard interval inserted by GI insertion section  104 . A GI insertion section  106  inserts in the transmit signal a guard interval longer than the guard intervals inserted by GI insertion section  104  and GI insertion section  105 . Based on the retransmission information input from control section  101 , selection section  107  selects a transmit signal in which a longer guard interval has been inserted as the number of retransmissions increases. By this means it is possible to prevent an increase in transmission delay due to an excessive increase in the number of retransmissions with almost no lowering of transmission efficiency.

TECHNICAL FIELD

The present invention relates to a transmitting apparatus andtransmitting method using a multicarrier transmission method such asOFDM (Orthogonal Frequency Division Multiplexing).

BACKGROUND ART

Generally, in an OFDM transmitting/receiving apparatus, a frameconfiguration is used in which a signal with the same waveform as thelast part of effective symbols is added as a guard interval (hereinafterreferred to as “GI”) at the start of effective symbols. A delayedwaveform with a delay time shorter than the guard interval length can beeliminated by Fast Fourier Transformation (hereinafter referred to as“FFT”) processing in the receiving system. On the other hand, if themultipath delay time is longer than the GI length, or if there is timingerror, the preceding signal may leak into the effective symbols of thenext signal, and inter-code interference may occur.

In the transmitting system, a signal that has undergone Inverse FastFourier Transform (hereinafter referred to as “IFFT”) processing has aGI inserted and is converted from a digital signal to an analog signal,and a transmit signal is obtained.

In the receiving system, a received signal is converted from an analogsignal to a digital signal. Then the received signal from which GIs havebeen eliminated by a GI elimination circuit undergoes FFT processing,and a baseband signal is obtained. The baseband signal undergoescoherent detection by means of a coherent detector, and a coherentdetected signal is obtained.

Nowadays, in radio communications, and especially in mobilecommunications, various kinds of information such as images and data aretransmitted as well as voice. Henceforth, demand for the transmission ofvarious kinds of content is expected to continue to grow, furtherincreasing the necessity of highly reliable, high-speed transmission.However, when high-speed transmission is carried out in mobilecommunications, the effect of delayed waves due to multipath propagationcan no longer be ignored, and transmission characteristics degrade dueto frequency selective fading.

Multicarrier (MC) modulation methods such as OFDM (Orthogonal FrequencyDivision Multiplexing) are attracting attention as one kind oftechnology for combating frequency selective fading. A multicarriermodulation method is a technology for effectively performing high-speedtransmission by transmitting data using a plurality of carrier waves(subcarriers) whose speed is suppressed to a level at which frequencyselective fading does not occur. With the OFDM method, in particular,the subcarriers to which data is allocated are mutually orthogonal,making this the multicarrier modulation method offering the highestspectral efficiency. Moreover, the OFDM method can be implemented with acomparatively simple hardware configuration. For these reasons, the OFDMmethod has attracted particular attention and is the subject of variousstudies.

Conventionally, received signal transmission error detection isperformed, and when an error is detected, a retransmission requestsignal is sent to the communicating radio station. On receiving aretransmission request, the communicating radio station retransmits datacorresponding to the retransmission request. This processing is thenrepeated until there is no longer an error in the received signal. Thisseries of processes is called ARQ.

However, with a conventional transmitting apparatus and transmittingmethod, particularly when channel fluctuations are slow, errors mayoccur consecutively even when retransmission is performed to a specificuser requesting retransmission. In this case the number ofretransmissions increases excessively, and since propagation delayincreases as the number of retransmissions increases, there is a problemof increased transmission delay. There is a method for preventing thisincrease in transmission delay by discontinuing retransmissions at agiven delay time, but in this case, there is a problem of error ratedegradation. Furthermore, since new data is not contained in a GI, thereis also a problem of transmission efficiency decreasing as a GI is madelonger.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a transmittingapparatus and transmitting method that make it possible to prevent anincrease in transmission delay due to an excessive increase in thenumber of retransmissions.

This object is achieved by increasing the GI length in proportion as thenumber of retransmissions increases, or taking delay distributioninformation, the transmission time interval, the band used, or the like,into consideration in setting the GI length. Also, this object isachieved by increasing only the GI length for systematic bit data outputby turbo coding when the number of retransmissions increases.Furthermore, this object is achieved by increasing the number ofsubcarriers to which the same signal is allocated in proportion as thenumber of retransmissions increases, or taking channel qualityinformation, the transmission time interval, the band used, or the like,into consideration in setting the number of subcarriers to which thesame signal is allocated. Moreover, this object is achieved byincreasing only the number of subcarriers to which the same signal ofsystematic bit data output by turbo coding is allocated when the numberof retransmissions increases.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing the configuration of a transmittingapparatus according to Embodiment 1 of the present invention;

FIG. 2 is a drawing showing signal arrangement in an OFDM-CDMAcommunication method;

FIG. 3 is a flowchart showing the operation of a transmitting apparatusaccording to Embodiment 1 of the present invention;

FIG. 4 is a drawing of a transmit signal with a GI inserted;

FIG. 5 is a drawing of a transmit signal with a GI inserted;

FIG. 6 is a drawing of a transmit signal with a GI inserted;

FIG. 7 is a block diagram showing the configuration of a transmittingapparatus according to Embodiment 2 of the present invention;

FIG. 8 is a flowchart showing the operation of a transmitting apparatusaccording to Embodiment 2 of the present invention;

FIG. 9 is a block diagram showing the configuration of a transmittingapparatus according to Embodiment 3 of the present invention;

FIG. 10 is a block diagram showing the configuration of a delaydistribution information generation section;

FIG. 11 is a flowchart showing the operation of a transmitting apparatusaccording to Embodiment 3 of the present invention;

FIG. 12 is a block diagram showing the configuration of a transmittingapparatus according to Embodiment 4 of the present invention;

FIG. 13 is a flowchart showing the operation of a transmitting apparatusaccording to Embodiment 4 of the present invention;

FIG. 14 is a block diagram showing the configuration of a transmittingapparatus according to Embodiment 5 of the present invention;

FIG. 15 is a flowchart showing the operation of a transmitting apparatusaccording to Embodiment 5 of the present invention;

FIG. 16 is a block diagram showing the configuration of a transmittingapparatus according to Embodiment 6 of the present invention;

FIG. 17 is a flowchart showing the operation of a transmitting apparatusaccording to Embodiment 6 of the present invention;

FIG. 18 is a drawing showing transmit signal rearrangement;

FIG. 19 is a drawing showing transmit signal rearrangement;

FIG. 20 is a drawing showing transmit signal rearrangement;

FIG. 21 is a drawing showing signal assignment to subcarriers;

FIG. 22 is a drawing showing signal assignment to subcarriers;

FIG. 23 is a drawing showing signal assignment to subcarriers;

FIG. 24 is a block diagram showing the configuration of a transmittingapparatus according to Embodiment 7 of the present invention;

FIG. 25 is a flowchart showing the operation of a transmitting apparatusaccording to Embodiment 7 of the present invention;

FIG. 26 is a block diagram showing the configuration of a transmittingapparatus according to Embodiment 8 of the present invention;

FIG. 27 is a flowchart showing the operation of a transmitting apparatusaccording to Embodiment 8 of the present invention;

FIG. 28 is a block diagram showing the configuration of a transmittingapparatus according to Embodiment 9 of the present invention;

FIG. 29 is a flowchart showing the operation of a transmitting apparatusaccording to Embodiment 9 of the present invention;

FIG. 30 is a block diagram showing the configuration of a transmittingapparatus according to Embodiment 10 of the present invention;

FIG. 31 is a flowchart showing the operation of a transmitting apparatusaccording to Embodiment 10 of the present invention; and

FIG. 32 is a block diagram showing the configuration of a transmittingapparatus according to Embodiment 11 of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference now to the accompanying drawings, embodiments of thepresent invention will be explained in detail below.

Embodiment 1

FIG. 1 is a block diagram showing the configuration of a transmittingapparatus according to Embodiment 1 of the present invention.

Transmitting apparatus 100 is mainly composed of a control section 101,a spreading section 102, an IFFT section 103, a GI insertion section104, a GI insertion section 105, a GI insertion section 106, a selectionsection 107, and an antenna 108.

Control section 101 temporarily stores a transmit signal modulated by amodulation section (not shown), and when transmission timing is reached,outputs the transmit signal to spreading section 102. As there are twocases for a transmit signal—the case of a normal transmit signal that isnot a retransmission signal, and the case of a retransmissionsignal—control section 101 separates transmit signals intoretransmission signals and normal signals other than retransmissionsignals, determines the retransmission count in the case of aretransmission signal, and outputs retransmission information toselection section 107. Retransmission information includes informationas to whether this is a retransmission, and information on theretransmission count.

Spreading section 102 carries out spreading processing of transmitsignals input from control section 101 using different spreading codes,performs code division multiplexing, and generates a CDMA signal, whichit outputs to IFFT section 103. As spreading ratio 1, spreading section102 may output a transmit signal directly to IFFT section 103 withoutspreading that transmit signal. In this case, the signal subject to IFFTprocessing by IFFT section 103 is an OFDM signal.

IFFT section 103, which is an orthogonal frequency division multiplexingsection, performs IFFT processing of a transmit signal input fromspreading section 102, generates an OFDM-CDMA signal, and outputs thisOFDM-CDMA signal to GI insertion sections 104, 105, and 106. As shown inFIG. 2, an OFDM-CDMA signal can be generated by assigning one spreadingcode chip to one subcarrier. FIG. 2 shows a case in which allsubcarriers are divided into four groups, G1 through G4. Any codemultiplexing number, such as code multiplexing number 1, can be selectedfor an OFDM-CDMA signal generated by IFFT section 103. Here, the codemultiplexing number is the number of multiplexings per carrier, and isdetermined by the number of users (codes) multiplexed. Therefore, in thecase of code multiplexing number 1, only one user is assigned to onesubcarrier.

GI insertion section 104 inserts a GI into a transmit signal input fromIFFT section 103, and after GI insertion, outputs the transmit signal toselection section 107. The length of the GI inserted by GI insertionsection 104 is shorter than for GI insertion section 105 and GIinsertion section 106.

GI insertion section 105 inserts a GI into the transmit signal inputfrom IFFT section 103, and after GI insertion, outputs the transmitsignal to selection section 107. The length of the GI inserted by GIinsertion section 105 is longer than the length of a GI inserted by GIinsertion section 104, and shorter than the length of a GI inserted byGI insertion section 106. GI insertion section 105 can set the length ofa GI inserted into a transmit signal arbitrarily, as long as that lengthis longer than the length of a GI inserted by GI insertion section 104,and shorter than the length of a GI inserted by GI insertion section106, and also may insert a GI of a length that is an integral multipleof the length of a GI inserted by GI insertion section 104.

GI insertion section 106 inserts a GI into the transmit signal inputfrom IFFT section 103, and after GI insertion, outputs the transmitsignal to selection section 107. The length of the GI inserted by GIinsertion section 106 is longer than for GI insertion section 104 and GIinsertion section 105. GI insertion section 106 can set the length of aGI inserted into a transmit signal arbitrarily, as long as that lengthis longer than the length of GIs inserted by GI insertion section 104and GI insertion section 105, and also may insert a GI of a length thatis an integral multiple of the length of a GI inserted by GI insertionsection 104.

Based on retransmission count information input from control section101, selection section 107 selects one from among the transmit signalswith a GI inserted input from GI insertion section 104, GI insertionsection 105, and GI insertion section 106, and transmits the selectedtransmit signal from antenna 108. In transmit signal selection, based onretransmission count information, the transmit signal input from GIinsertion section 104 is selected in the case of transmission that isnot a retransmission, the transmit signal input from GI insertionsection 105 is selected in the case of a first retransmission, and thetransmit signal input from GI insertion section 106 is selected in thecase of a second retransmission.

The operation of transmitting apparatus 100 will now be described usingFIG. 3 through FIG. 6. First, a transmit signal is determined to beeither a retransmission signal or a normal signal other than aretransmission signal by control section 101 (step (hereinafter referredto as “ST”) 301). Furthermore, if the transmit signal is aretransmission signal, whether or not this is the first retransmissionis determined by control section 101 (ST302). Control section 101 thenoutputs retransmission information containing information as to whetheror not this is a retransmission signal and retransmission countinformation to selection section 107.

Next, an OFDM-CDMA signal that has undergone spreading processing byspreading section 102 and IFFT processing by IFFT section 103 has a GIinserted by GI insertion section 104, GI insertion section 105, and GIinsertion section 106. If the lengths of GIs inserted by GI insertionsection 105 and GI insertion section 106 are made integral multiples ofthe length of a GI inserted by GI insertion section 104, it is onlynecessary for the signal waveform of a GI inserted by GI insertionsection 104 to be repeated a given number of times, and thereforeprocessing for inserting GIs can be simplified, and there will be noincomplete leftovers when OFDM symbols are rearranged up to the end of aframe, as compared with the case where the GI length is not an integralmultiple, making it possible to prevent processing from becomingcumbersome.

As shown in FIG. 4, a transmit signal in which a GI has been inserted byGI insertion section 104 includes a GI length Tg1 that is one-eighth ofeffective symbol length Ts1. Also, as shown in FIG. 5, a transmit signalin which a GI has been inserted by GI insertion section 105 includes aGI length Tg2 that is one-fourth of effective symbol length Ts2.Furthermore, as shown in FIG. 6, a transmit signal in which a GI hasbeen inserted by GI insertion section 106 includes a GI length Tg3 thatis three-eighths of effective symbol length Ts3.

Based on retransmission information input from control section 101,selection section 107 selects a transmit signal input from GI insertionsection 104, 105, or 106. That is to say, if the transmit signal to betransmitted is not a retransmission signal, a transmit signal input fromGI insertion section 104 is selected in which, as shown in FIG. 4, a GIlength Tg1 that is one-eighth of effective symbol length Ts1 has beeninserted (ST303).

If, based on retransmission information input from control section 101,this transmission is a first retransmission, selection section 107selects a transmit signal input from GI insertion section 105 in which,as shown in FIG. 5, a GI length Tg2 that is one-fourth of effectivesymbol length Ts2 has been inserted (ST304), and if this transmission isa second retransmission, selection section 107 selects a transmit signalinput from GI insertion section 106 in which, as shown in FIG. 6, a GIlength Tg3 that is three-eighths of effective symbol length Ts3 has beeninserted (ST305).

Selection section 107 then outputs the selected transmit signal (ST306).As described above, the GI length increases in proportion as the numberof retransmissions increases. The relationship between GI lengths isTg1>Tg2>Tg3, and GIs are set longer in the order of FIG. 4, FIG. 5, andFIG. 6.

Thus, according to Embodiment 1, a selection section selects a transmitsignal with a longer GI as the number of retransmissions increases,based on retransmission information input from a control section, sothat the error rate improvement effect is heightened, and it is possibleto prevent an increase in transmission delay due to an excessiveincrease in the number of retransmissions with almost no lowering oftransmission efficiency. Also, delay time becomes shorter than the GIlength as a result of increasing the GI length as the number ofretransmissions increases, enabling inter-code interference to bereduced in a multipath environment.

Embodiment 2

FIG. 7 is a drawing showing the configuration of a transmittingapparatus 700 according to Embodiment 2 of the present invention. Afeature of this embodiment is that GI lengths are set separately forsystematic bit data and parity bit data. In this embodiment, theconfiguration in FIG. 7 differs from that in FIG. 1 in including a turbocoding section 701, a parallel/serial (hereinafter referred to as “P/S”)conversion section 702, and a modulation section 703. Parts in FIG. 7identical to those in FIG. 1 are assigned the same codes as in FIG. 1,and descriptions thereof are omitted.

When turbo code is used as an error correction code, systematic bit dataand parity bit data are output, and better quality is required forsystematic bit data. Therefore, by making the GI length of systematicbit data longer than the GI length of parity bit data, it is possible tofurther achieve compatibility between transmission efficiency and theerror rate.

Control section 101 temporarily stores transmit signals, and separatestransmit signals into retransmission signals and normal signals otherthan retransmission signals. Then, when transmission timing is reached,control section 101 outputs a transmit signal to spreading section 102,and also outputs retransmission information to selection section 107.Retransmission information includes retransmission count information.Control section 101 also controls the transmission timing at whichsystematic bit data and parity bit data are output, and outputsinformation as to whether a transmit signal is systematic bit data orparity bit data to selection section 107.

Turbo coding section 701 outputs part of a transmit signal input fromcontrol section 101 uncoded to P/S conversion section 702 as systematicbit data, and also performs recursive convolutional coding on theremaining part of the input transmit signal and outputs this part to P/Sconversion section 702 as parity bit data.

P/S conversion section 702, which is an allocation section, convertssystematic bit data and parity bit data input from turbo coding section701 from parallel data format to serial data format, and outputs thesedata to modulation section 703. Systematic bit data and parity bit dataconverted by P/S conversion section 702 is made up of all systematicbits or parity bits on a symbol-by-symbol basis.

Modulation section 703, which is an allocation section, modulatessystematic bits or parity bits of each symbol input from P/S conversionsection 702 and outputs the result to spreading section 102.

GI insertion sections 104, 105, and 106 insert GIs independently forsystematic bit data and parity bit data. In this case, the length of aGI inserted in parity bit data may be shorter than the length of a GIinserted in systematic bit data, and furthermore the GI length of paritybit data may be made the same irrespective of the number ofretransmissions, and the GI length of systematic bit data may beincreased as the number of retransmissions increases.

Based on information indicating the retransmission count and whether ornot the transmit data is systematic bit data or parity bit data inputfrom control section 101, selection section 107 selects one from amongthe transmit signals with a GI inserted input from GI insertion section104, GI insertion section 105, and GI insertion section 106, andtransmits the selected transmit signal from antenna 108. That is to say,control is performed so that if the transmit data is systematic bitdata, the GI length is increased as the number of retransmissionsincreases, and if the transmit data is parity bit data, the GI lengthdoes not change even if the number of retransmissions increases.

The operation of transmitting apparatus 700 will now be described usingFIG. 4, FIG. 5, FIG. 6, and FIG. 8. Control section 101 determineswhether or not a transmit signal is systematic bit data (ST801), andoutputs information as to whether or not the transmit data is systematicbit data to selection section 107. If the transmit data is systematicbit data, control section 101 determines whether or not this is aretransmission (ST802), and in the case of a retransmission furtherdetermines whether or not this is the first retransmission (ST803), andoutputs retransmission information including information as to whetheror not the transmit signal is a retransmission signal and, if thetransmit signal is a retransmission signal, retransmission countinformation, to selection section 107.

Based on information as to whether or not the transmit signal issystematic bit data, input from control section 101, if the transmitsignal is not systematic bit data but parity bit data, selection section107 selects a transmit signal input from GI insertion section 104 inwhich, as shown in FIG. 4, a GI length Tg1 that is one-eighth ofeffective symbol length Ts1 has been inserted (ST804). If parity bitdata GI length Tg1 is fixed at one-eighth of effective symbol lengthTs1, and only the length of the GI inserted in a systematic bit datatransmit signal for which good quality is required is changed, it ispossible to improve error rate characteristics without loweringtransmission efficiency, and to achieve compatibility betweentransmission efficiency and error rate characteristics.

Also, based on information as to whether or not the transmit signal issystematic bit data and retransmission information, if the transmitsignal is systematic bit data and the transmit signal is not aretransmission signal, selection section 107 selects a transmit signalinput from GI insertion section 104 in which, as shown in FIG. 4, a GIlength Tg1 that is one-eighth of effective symbol length Ts1 has beeninserted (ST804).

Furthermore, if, based on retransmission information input from controlsection 101, this transmission is a first retransmission, selectionsection 107 selects a transmit signal input from GI insertion section105 in which, as shown in FIG. 5, a GI length Tg2 that is one-fourth ofeffective symbol length Ts2 has been inserted (ST805), and if thistransmission is a second retransmission, selection section 107 selects atransmit signal input from GI insertion section 106 in which, as shownin FIG. 6, a GI length Tg3 that is three-eighths of effective symbollength Ts3 has been inserted (ST806).

Selection section 107 then outputs the transmit signal (ST807).

Thus, according to Embodiment 2, in addition to provision of the effectsof Embodiment 1 described above, turbo coding of transmit data isperformed by a turbo coding section that enables much better error ratecharacteristics to be obtained that with other error correction methods,and a selection section increases the length of a GI inserted insystematic bit data as the number of retransmissions increases, enablingerror rate characteristics to be significantly improved.

In this embodiment, the length of a GI inserted in systematic bit datain the case of retransmission is made longer than a GI inserted inparity bit data, but this is not a limitation, and the length of a GIinserted in systematic bit data in the case of retransmission may bemade the same as the length of a GI inserted in parity bit data.

Embodiment 3

FIG. 9 is a drawing showing the configuration of a transmittingapparatus 900 according to Embodiment 3 of the present invention. Afeature of this embodiment is that the length of a GI is selected takingdelay distribution information into consideration. In this embodiment,the configuration in FIG. 9 differs from that in FIG. 1 in including aturbo coding section 901 and a P/S conversion section 902. Parts in FIG.9 identical to those in FIG. 1 are assigned the same codes as in FIG. 1,and descriptions thereof are omitted.

The length of a GI can generally be determined according to delaydistribution. Therefore, if delay distribution information is reflectedin determining GI length, it is possible to further achievecompatibility between transmission efficiency and the error rate.

Control section 101 temporarily stores transmit signals, and separatestransmit signals into retransmission signals and normal signals otherthan retransmission signals. Then, when transmission timing is reached,control section 101 outputs a transmit signal to spreading section 102,and also outputs retransmission information to selection section 107.Retransmission information includes retransmission count information.Control section 101 also outputs delay distribution information toselection section 107. Delay distribution information is reported bybeing included in a transmit signal from the communicating party, and istherefore extracted from a received signal. The configuration of a delaydistribution generation section on the communicating party side will bedescribed later herein.

Turbo coding section 901 outputs part of a transmit signal input fromcontrol section 101 uncoded to P/S conversion section 902 as systematicbit data, and also performs recursive convolutional coding on theremaining part of the input transmit signal and outputs this part to P/Sconversion section 902 as parity bit data.

P/S conversion section 902 converts systematic bit data and parity bitdata input from turbo coding section 901 from parallel data format toserial data format, and outputs these data to modulation section 903.

Based on retransmission count information and delay distributioninformation input from control section 101, selection section 107selects one from among the transmit signals with a GI inserted inputfrom GI insertion section 104, GI insertion section 105, and GIinsertion section 106, and transmits the selected transmit signal fromantenna 108. That is to say, if delay distribution is small, thetransmit signal input from GI insertion section 105 will be selectedeven if the transmission is a second retransmission.

The operation of delay distribution information generation section 1000will now be described using FIG. 10. Delay distribution informationgeneration section 1000 is mainly composed of a delay circuit 1001, asubtraction circuit 1002, an absolute value generation circuit 1003, andan averaging circuit 1004.

Delay circuit 1001 has as input a signal in which the preamble of areceived signal has undergone FFT processing, applies delay to the inputsignal, and outputs the signal to subtraction circuit 1002.

Subtraction circuit 1002 calculates the difference in signal levels ofadjacent subcarriers, and outputs the result to absolute valuegeneration circuit 1003.

Absolute value generation circuit 1003 converts the subtraction resultinput from subtraction circuit 1002 to an absolute value, and outputsthis absolute value to averaging circuit 1004.

Averaging circuit 1004 averages absolute values of reception leveldifferences input from absolute value generation circuit 1003 for thenumber of subcarriers, and delay distribution information is obtained.The delay distribution information obtained in this way is transmittedincluded in a transmit signal by the communicating party.

Delay distribution information is not limited to the case where it isfound by a communicating party and reported by the communicating party,and delay distribution may be detected from the circuit in FIG. 10 usinga received signal. The case where delay distribution is detected from areceived signal is possible with the TDD communication method or thelike.

The operation of transmitting apparatus 900 will now be described usingFIG. 4, FIG. 5, FIG. 6, and FIG. 11. Control section 101 determineswhether or not a transmit signal is a retransmission signal (ST1101),and in the case of a retransmission further determines whether or notthis is the first retransmission (ST1102), and outputs retransmissioninformation including information as to whether or not the transmitsignal is a retransmission signal and, if the transmit signal is aretransmission signal, retransmission count information, to selectionsection 107. Control section 101 also outputs delay distributioninformation reported from the communicating party, included in thereceived signal, to selection section 107.

Based on retransmission information input from control section 101, ifthe transmit signal to be transmitted is not a retransmission signal,selection section 107 selects a transmit signal in which, as shown inFIG. 4, a GI length Tg1 that is one-eighth of effective symbol lengthTs1 has been inserted (ST1103).

Based on retransmission information input from control section 101, ifthis transmission is a first retransmission, selection section 107selects a transmit signal in which, as shown in FIG. 5, a GI length Tg2that is one-fourth of effective symbol length Ts2 has been inserted(ST1104), and if this transmission is a second retransmission, selectionsection 107 determines from the delay distribution information inputfrom control section 101 whether or not the delay distribution is lessthan a threshold value (ST1105).

If the delay distribution is less than the threshold value, selectionsection 107 selects a transmit signal in which, as shown in FIG. 5, a GIlength Tg2 that is one-fourth of effective symbol length Ts2 has beeninserted (ST1104), and if the delay distribution is greater than orequal to the threshold value, selection section 107 selects a transmitsignal in which, as shown in FIG. 6, a GI length Tg3 that isthree-eighths of effective symbol length Ts3 has been inserted (ST1106).

Selection section 107 then outputs a transmit signal in which theselected GI length has been inserted (ST1107).

Thus, according to Embodiment 3, in addition to provision of the effectsof Embodiment 1 described above, a selection section selects a transmitsignal that includes a GI of a length that takes delay distributioninformation into consideration, so that if GI length need not beincreased much even though the number of retransmissions increases, atransmit signal with an unnecessarily long GI is not selected, andtransmission efficiency can be improved to the greatest extent possible.

In this embodiment, the magnitude of delay distribution is determined atthe time of a second retransmission, but this is not a limitation, andthe magnitude of delay distribution may be determined at the time of afirst retransmission.

Embodiment 4

FIG. 12 is a drawing showing the configuration of a transmittingapparatus 1200 according to Embodiment 4 of the present invention. Afeature of this embodiment is that the length of a GI is selected takingthe transmission time interval into consideration. In this embodiment,the configuration in FIG. 12 differs from that in FIG. 1 in including acounter section 1201, a delay section 1202, and a subtraction section1203. Parts in FIG. 12 identical to those in FIG. 1 are assigned thesame codes as in FIG. 1, and descriptions thereof are omitted.

When CSMA (Carrier Sense Multiple Access) is used as an access method,as in IEEE802.11, if a channel is congested the time interval betweenthe previous transmission and the present transmission may be very long.In such cases, transmission delay may be extremely long if there is anerror in a second or third retransmission. An effective method ofpreventing this problem is to select GI length taking the transmissiontime interval between the previous transmission and the presenttransmission into consideration. In CSMA, a terminal performs carriersensing and transmits if the reception level is less than or equal to athreshold value.

Counter section 1201 generates information indicating transmissiontiming based on transmission timing input from control section 101, andoutputs this generated information to delay section 1202 and subtractionsection 1203.

Delay section 1202 delays the information indicating transmission timinginput from counter section 1201, and outputs this information tosubtraction section 1203.

From the information indicating transmission timing input from countersection 1201 and the transmission timing input from delay section 1202,subtraction section 1203 calculates the difference between thetransmission timing of the previous transmission and the transmissiontiming of the present transmission, and outputs the calculatedtransmission timing difference to selection section 107 as atransmission time interval.

Based on retransmission count information input from control section 101and information indicating the transmission time interval input fromsubtraction section 1203, selection section 107 selects one from amongthe transmit signals with a GI inserted input from GI insertion section104, GI insertion section 105, and GI insertion section 106, andtransmits the selected transmit signal from antenna 108. That is to say,if the transmission time interval is large, the transmit signal inputfrom GI insertion section 106, which has the longest GI of the threekinds of GI, will be selected even in the case of a firstretransmission.

The operation of transmitting apparatus 1200 will now be described usingFIG. 4, FIG. 5, FIG. 6, and FIG. 13. Control section 101 determineswhether or not a transmit signal is a retransmission signal (ST1301),and in the case of a retransmission further determines whether or notthis is the first retransmission (ST1302), and outputs retransmissioninformation including information as to whether or not the transmitsignal is a retransmission signal and, if the transmit signal is aretransmission signal, retransmission count information, to selectionsection 107. Control section 101 also outputs information indicating thecalculated transmission time interval to selection section 107.

Based on retransmission information input from control section 101, ifthe transmit signal to be transmitted is not a retransmission signal,selection section 107 selects a transmit signal in which, as shown inFIG. 4, a GI length Tg1 that is one-eighth of effective symbol lengthTs1 has been inserted (ST1303).

Based on retransmission information input from control section 101, ifthis transmission is a first retransmission, selection section 107determines whether or not the transmission time interval is greater thanor equal to a threshold value (ST1304), and if this transmission is asecond retransmission, selection section 107 selects a transmit signalin which, as shown in FIG. 6, a GI length Tg3 that is three-eighths ofeffective symbol length Ts3 has been inserted (ST1306).

If the transmission time interval input from control section 101 is lessthan the threshold value, selection section 107 selects a transmitsignal in which, as shown in FIG. 5, a GI length Tg2 that is one-fourthof effective symbol length Ts2 has been inserted (ST1305), and if thetransmission time interval is greater than or equal to the thresholdvalue, selection section 107 selects a transmit signal in which, asshown in FIG. 6, a GI length Tg3 that is three-eighths of effectivesymbol length Ts3 has been inserted (ST1306).

Selection section 107 then outputs a transmit signal in which theselected GI length has been inserted (ST1307).

Thus, according to Embodiment 4, in addition to provision of the effectsof Embodiment 1 described above, a selection section selects a transmitsignal that includes a GI of a length that takes the transmission timeinterval into consideration, making it possible to prevent transmissiondelay from becoming extremely long due to numerous retransmissions whenthe transmission time interval is long.

In this embodiment, the length of the transmission time interval iscompared at the time of a first retransmission, but this is not alimitation, and the length of the transmission time interval may becompared at the time of a transmission that is not a retransmission.

Embodiment 5

FIG. 14 is a drawing showing the configuration of a transmittingapparatus 1400 according to Embodiment 5 of the present invention. Afeature of this embodiment is that the length of a GI is selected takingthe band usage situation into consideration. Parts in FIG. 14 identicalto those in FIG. 1 are assigned the same codes as in FIG. 1, anddescriptions thereof are omitted.

If information on the band usage situation is reported from thecommunicating party, or the band whose use is permitted is known as ausable bandwidth, control section 101 can ascertain how much of a marginthere is in the remaining band from the used band currently being used,and outputs information on the ratio of the used band to the band whoseuse is permitted to selection section 107.

Based on retransmission count information and information indicating theband usage situation input from control section 101, selection section107 selects one from among the transmit signals with a GI inserted inputfrom GI insertion section 104, GI insertion section 105, and GIinsertion section 106, and transmits the selected transmit signal fromantenna 108. That is to say, if there is a margin in the band, thetransmit signal input from GI insertion section 106, which has thelongest GI of the three kinds of GI, will be selected even in the caseof a first retransmission.

The operation of transmitting apparatus 1400 will now be described usingFIG. 4, FIG. 5, FIG. 6, and FIG. 15. Control section 101 determineswhether or not a transmit signal is a retransmission signal (ST1501),and in the case of a retransmission further determines whether or notthis is the first retransmission (ST1502), and outputs retransmissioninformation including information as to whether or not the transmitsignal is a retransmission signal and, if the transmit signal is aretransmission signal, retransmission count information, to selectionsection 107. Control section 101 also outputs information indicating theband usage situation for each communicating party to selection section107.

Based on retransmission information input from control section 101, ifthe transmit signal to be transmitted is not a retransmission signal,selection section 107 selects a transmit signal in which, as shown inFIG. 4, a GI length Tg1 that is one-eighth of effective symbol lengthTs1 has been inserted (ST1503).

Based on retransmission information and information indicating the bandusage situation input from control section 101, if this transmission isa first retransmission, selection section 107 determines whether or notthe ratio of the used band to the band whose use is permitted is lessthan or equal to a threshold value (ST1504), and if this transmission isa second retransmission, selection section 107 selects a transmit signalin which, as shown in FIG. 6, a GI length Tg3 that is three-eighths ofeffective symbol length Ts3 has been inserted (ST1506).

If the ratio of the used band to the band whose use is permitted isgreater than the threshold value, selection section 107 selects atransmit signal in which, as shown in FIG. 5, a GI length Tg2 that isone-fourth of effective symbol length Ts2 has been inserted (ST1505),and if the ratio of the used band to the band whose use is permitted isless than or equal to the threshold value, selection section 107 selectsa transmit signal in which, as shown in FIG. 6, a GI length Tg3 that isthree-eighths of effective symbol length Ts3 has been inserted (ST1506).Thus selection section 107 selects a transmit signal in which a GI hasbeen inserted that depends on the used band, so that when there is aused band margin the GI can be made longer without lowering transmissionefficiency, and when there is not much of a margin in the used bandcontrol can be performed so that the GI is not made unnecessarily long,making it possible to prevent a decrease in transmission efficiency.

Selection section 107 then outputs a transmit signal in which theselected GI length has been inserted (ST1507).

Thus, according to Embodiment 5, in addition to provision of the effectsof Embodiment 1 described above, a selection section selects a transmitsignal in which a GI of a length that depends on the band usagesituation has been inserted, making it possible to prevent transmissiondelay without lowering transmission efficiency.

In this embodiment, the ratio of the used band to the band whose use ispermitted is determined at the time of a first retransmission, but thisis not a limitation, and the ratio of the used band to the band whoseuse is permitted may be determined at the time of a transmission that isnot a retransmission.

Embodiment 6

FIG. 16 is a block diagram showing part of the configuration of atransmitting apparatus according to Embodiment 6 of the presentinvention.

Transmitting apparatus 1600 is mainly composed of a control section1601, a serial/parallel (hereinafter referred to as “S/P”) conversionsection 1603, a P/S conversion section 1604, an IFFT section 1605, a GIinsertion section 1606, and an antenna 1607.

Control section 1601 temporarily stores transmit signals modulated by amodulation section (not shown) and separates transmit signals intoretransmission information and normal information other thanretransmission information. Then, when transmission timing is reached,control section 1601 outputs a transmit signal to spreading section1602, and also outputs retransmission information to S/P conversionsection 1603 and P/S conversion section 1604. Retransmission informationincludes information on the retransmission count and data to beretransmitted.

Spreading section 1602 carries out spreading processing of transmitsignals input from control section 1601 using different spreading codes,performs code division multiplexing, and generates a CDMA signal, whichis output to S/P conversion section 1603. As spreading ratio 1,spreading section 1602 may output a transmit signal directly to IFFTsection 103 without spreading that transmit signal. In this case, thesignal processed by IFFT section 103 is an OFDM signal.

When retransmission information input from control section 1601indicates a normal transmission, not a retransmission, S/P conversionsection 1603, which is a rearranging section, converts the transmitsignal input from spreading section 1602 directly from serial dataformat to parallel data format, and outputs the resulting signal to P/Sconversion section 1604. On the other hand, when retransmissioninformation input from control section 1601 indicates a retransmission,S/P conversion section 1603 converts the transmit signal to paralleldata format and stores it in memory, and reads data to be retransmittedcontained in the retransmission information from memory a number oftimes in accordance with the retransmission count, and outputs this datato P/S conversion section 1604.

In a first transmission, P/S conversion section 1604, which is arearranging section, converts a transmit signal input from S/Pconversion section 1603 directly from parallel data format to serialdata format, and outputs this signal to IFFT section 1605. On the otherhand, in a retransmission, P/S conversion section 1604 performsrearrangement of a transmit signal including retransmission data inputfrom S/P conversion section 1603 according to retransmission informationinput from control section 1601, and outputs the rearranged transmitsignal to IFFT section 1605. The method of rearranging the transmitsignal will be described later herein.

IFFT section 1605, which is an orthogonal frequency divisionmultiplexing section, performs orthogonal frequency divisionmultiplexing processing such as IFFT processing of a transmit signalinput from GI insertion section 104, generates an OFDM-CDMA signal, andoutputs this OFDM-CDMA signal to GI insertion section 106. An OFDM-CDMAsignal can be generated by assigning one spreading code chip to onesubcarrier. Any code multiplexing number, such as code multiplexingnumber 1, can be selected for an OFDM-CDMA signal generated by IFFTsection 103. Here, the code multiplexing number is the number ofmultiplexings per carrier, and is determined by the number of users(codes) multiplexed. Therefore, in the case of code multiplexing number1, only one user is assigned to one subcarrier.

GI insertion section 1606 inserts a predetermined GI into a transmitsignal input from IFFT section 1605, and transmits the transmit signalfrom antenna 1607. A radio section (not shown) is provided between GIinsertion section 106 and antenna 1607, and processing such asup-conversion from baseband frequency to radio frequency is performed bythis radio section.

The operation of transmitting apparatus 1600 will now be described usingFIG. 17 through FIG. 20. FIG. 17 is a flowchart showing the operation oftransmitting apparatus 1600, and FIG. 18 through FIG. 20 are drawingsshowing transmit signal rearrangement methods using S/P conversionsection 1603 and P/S conversion section 1604.

First, control section 1601 determines whether an input transmit signaldemodulated by a demodulation section (not shown) is a normalnon-retransmission signal or a retransmission signal (ST1701), and ifthe transmit signal is a retransmission signal, determines whether ornot this is the first retransmission (ST1702). Control section 1601 thenoutputs retransmission information comprising information as to whetherthe signal is a normal signal or a retransmission signal (hereinafterreferred to as “signal type information”), information as to the numberof retransmissions (hereinafter referred to as “count information”), andinformation as to which signal the communicating party is requesting tobe retransmitted (hereinafter referred to as “request information”), toS/P conversion section 1603 and P/S conversion section 1604.

In the case of a normal transmission—that is, a transmission that is nota retransmission—a transmit signal that has undergone spreadingprocessing by spreading section 1602 is converted from serial dataformat data sequence “$1, $2, $3, $4” to parallel data format by S/Pconversion section 1603, and stored temporarily in memory 1801, as shownin FIG. 18. Signal $1 through signal $4 are code division multiplexedsignals.

As the transmit signals output from S/P conversion section 1603 are in anormal transmission, they are not rearranged by P/S conversion section1604, and are arranged in memory 1802 in signal $1, $2, $3, $4 orderfrom the top of FIG. 18, then read sequentially from the top of FIG. 18,and converted to serial data format. The transmit signal output from P/Sconversion section 1604 is arranged as serial data format data sequence“$1, $2, $3, $4” (ST1703).

On the other hand, in the case of a first retransmission, a transmitsignal that has undergone spreading processing by spreading section 1602is converted from serial data format data sequence “$1, $2, $3, $4” toparallel data format by S/P conversion section 1603, and storedtemporarily in memory 1801, as shown in FIG. 19. Then, since, accordingto signal type information, count information, and request informationinput from control section 1601, this is a first retransmission andretransmission has been requested for signal $1, signal $1 is read twicefrom memory 1801 and signals $2 and $3 are read once each, and thesesignals are output to P/S conversion section 1604.

As shown in FIG. 19, the transmit signals output from S/P conversionsection 1603 are arranged in memory 1802 of P/S conversion section 1604in signal $1, $2, $1, $3 order from the top of FIG. 19, then readsequentially from the top of FIG. 19, and converted to serial dataformat. The transmit signal output from P/S conversion section 1604 isarranged as serial data format data sequence “$1, $2, $1, $3” (ST1705).In a retransmission, transmission may be performed with only a signalfor which there is a retransmission request assigned to subcarriers, butretransmission is not limited to the case where transmission isperformed with only a signal for which there is a retransmission requestassigned to subcarriers, and transmission may be performed with anysignal for which there is no retransmission request transmitted togetherwith a retransmission signal, assigned to different subcarriers.

In the case of a second retransmission, a transmit signal that hasundergone spreading processing by spreading section 1602 is convertedfrom serial data format data sequence “$1, $2, $3, $4” to parallel dataformat by S/P conversion section 1603, and stored temporarily in memory1801, as shown in FIG. 20. Then, since, according to signal typeinformation, count information, and request information input fromcontrol section 1601, this is a second retransmission and retransmissionhas been requested for signal $1, signal $1 only is read four times frommemory 1801 and output to P/S conversion section 1604.

As shown in FIG. 20, the transmit signals output from S/P conversionsection 1603 are arranged in memory 1802 of P/S conversion section 1604in signal $1, $1, $1, $1 order from the top of FIG. 20, then readsequentially from the top of FIG. 20, and converted to serial dataformat. The transmit signal output from P/S conversion section 1604 isarranged as serial data format data sequence “$1, $1, $1, $1” (ST1704).

The transmit signal then undergoes orthogonal frequency divisionmultiplexing processing such as IFFT processing by IFFT section 1605,and an OFDM-CDMA signal is obtained (ST1706).

The allocation of signals to subcarriers in an OFDM-CDMA signal obtainedin this way will now be described using FIG. 21 through FIG. 23.

With an OFDM-CDMA signal, the spreading ratio is made one-fourth of thenumber of subcarriers, and all the subcarriers are divided into foursubcarrier groups. That is to say, an OFDM-CDMA signal is divided into afirst group G1 composed of subcarrier #3 m+1 through subcarrier #4 m, asecond group G2 composed of subcarrier #2 m+1 through subcarrier #3 m, athird group G3 composed of subcarrier #m+1 through subcarrier #2 m, anda fourth group G4 composed of subcarrier #1 through subcarrier #m, andcode division multiplexed signals are arranged distributed amongsubcarrier groups on a group-by-group basis.

In normal (non-retransmission) transmission, as shown in FIG. 21 signal$1 is arranged distributed among the subcarriers of first group G1,signal $2 is arranged distributed among the subcarriers of second groupG2, signal $3 is arranged distributed among the subcarriers of thirdgroup G3, and signal $4 is arranged distributed among the subcarriers offourth group G4.

On the other hand, in a first retransmission, as shown in FIG. 22 signal$1 is arranged distributed among the subcarriers of first group G1 andin third group G3 signal $1 is arranged distributed among thesubcarriers in the same way as in first group G1, signal $2 is assignedto second group G2, and signal $3 is assigned to fourth group G4.Therefore, in a first retransmission, the number of subcarriers isdoubled as compared with a normal transmission by having signal $1assigned to the subcarriers of third group G3.

In a second retransmission, as shown in FIG. 23 signal $1 is arrangeddistributed among the subcarriers of first group G1, and in second groupG2, third group G3, and fourth group G4, also, signal $1 is arrangeddistributed among the subcarriers in the same way as in first group G1.Therefore, in a second retransmission, the number of subcarriers isdoubled compared with a first retransmission by having signal $1assigned to the subcarriers of second group G2 and the subcarriers offourth group G4.

If the number of subcarriers to which a retransmission signal isassigned is increased as the number of retransmissions increases, afrequency diversity effect can be obtained, and error ratecharacteristics can be improved. Also, since the number of subcarriersto which a retransmission signal is assigned increases by an integralmultiple of 2 each time as the number of retransmissions increases, inclock frequency division the frequency can be halved each time,simplifying clock generation, and data need only be added two at a timewhen receiving, simplifying received signal synthesis.

Thus, according to Embodiment 6, an S/P conversion section generates aretransmission signal based on retransmission information received froma control section, a P/S conversion section performs rearrangement of atransmit signal containing the generated retransmission signal, and thetransmit signal undergoes orthogonal frequency division multiplexing byan IFFT section, so that the number of subcarriers to which aretransmission signal is assigned increases as the number ofretransmissions increases, and it is possible to prevent an increase intransmission delay due to an excessive increase in the number ofretransmissions.

Embodiment 7

FIG. 24 is a drawing showing the configuration of a transmittingapparatus 2400 according to Embodiment 7 of the present invention. Afeature of this embodiment is that systematic bit data and parity bitdata are assigned to subcarriers separately. In this embodiment, theconfiguration in FIG. 24 differs from that in FIG. 16 in including aturbo coding section 2401 and a parallel/serial (hereinafter referred toas “P/S”) conversion section 2402. Parts in FIG. 24 identical to thosein FIG. 16 are assigned the same codes as in FIG. 16, and descriptionsthereof are omitted.

When turbo code is used as an error correction code, systematic bit dataand parity bit data are output, and better quality is required forsystematic bit data. Therefore, by making the number of subcarriers towhich systematic bit data is assigned greater than the number ofsubcarriers to which parity bit data is assigned, it is possible tofurther achieve compatibility between transmission efficiency and theerror rate.

Control section 1601 temporarily stores transmit signals, and separatestransmit signals into retransmission information and normal informationother than retransmission information. Then, when transmission timing isreached, control section 1601 outputs a transmit signal to spreadingsection 1602, and also outputs retransmission information to S/Pconversion section 1603 and P/S conversion section 1604. Retransmissioninformation comprises only signal type information in the case of anormal transmission, but comprises signal type information, countinformation, and request information in the case of a retransmission.Control section 1601 also controls the transmission timing at whichsystematic bit data and parity bit data are output, and outputsinformation as to whether a transmit signal is systematic bit data orparity bit data to S/P conversion section 1603 and P/S conversionsection 1604.

Turbo coding section 2401, which is a coding section, outputs part of atransmit signal input from control section 1601 uncoded to P/Sconversion section 2402 as systematic bit data, and also performsrecursive convolutional coding on the remaining part of the inputtransmit signal and outputs this part to P/S conversion section 2402 asparity bit data.

P/S conversion section 2402 converts systematic bit data and parity bitdata input from turbo coding section 2401 from parallel data format toserial data format, and outputs these data to spreading section 1602.Systematic bit data and parity bit data are allocated to differentsymbols.

The operation of transmitting apparatus 2400 will now be described usingFIG. 18 through FIG. 20 and FIG. 25. FIG. 25 is a flowchart showing theoperation of transmitting apparatus 2400.

First, control section 1601 determines whether or not a transmit signalis parity bit data (ST2501) and also determines whether or not this is aretransmission (ST2502), and in the case of a retransmission determineswhether or not this is the first retransmission (ST2504) Control section1601 then outputs information as to whether the transmit signal issystematic bit data or parity bit data (hereinafter referred to as “bitinformation”), and retransmission information comprising signal typeinformation, count information, and request information, to S/Pconversion section 1603 and P/S conversion section 1604.

If the transmit data is parity bit data, a transmit signal that hasundergone spreading processing by spreading section 1602 is convertedfrom serial data format parity bit data sequence “$1, $2, $3, $4” toparallel data format by S/P conversion section 1603, and storedtemporarily in memory 1801, as shown in FIG. 18.

As the transmit signals output from S/P conversion section 1603 are in anormal transmission, they are not rearranged by P/S conversion section1604, and are arranged in memory 1802 in parity bit data signal $1, $2,$3, $4 order from the top of FIG. 18, then read sequentially from thetop of FIG. 18, and converted to serial data format. The transmit signaloutput from P/S conversion section 1604 is arranged as serial dataformat parity bit data sequence “$1, $2, $3, $4” (ST2503).

On the other hand, if the transmit data is systematic bit data and thetransmission is a normal transmission (not a retransmission), a transmitsignal that has undergone spreading processing by spreading section 1602is converted from serial data format systematic bit data sequence “$1,$2, $3, $4” to parallel data format by S/P conversion section 1603, andstored temporarily in memory 1801, as shown in FIG. 18.

As the transmit signals output from S/P conversion section 1603 are in anormal transmission, they are not rearranged by P/S conversion section1604, and are arranged in memory 1802 in systematic bit data signal $1,$2, $3, $4 order from the top of FIG. 18, then read sequentially fromthe top of FIG. 18, and converted to serial data format. The transmitsignal output from P/S conversion section 1604 is arranged as serialdata format systematic bit data sequence “$1, $2, $3, $4” (ST2503).

If the transmit data is systematic bit data and the transmission is afirst retransmission, a transmit signal that has undergone spreadingprocessing by spreading section 1602 is converted from serial dataformat parity bit data sequence “$1, $2, $3, $4” to parallel data formatby S/P conversion section 1603, and stored temporarily in memory 1801,as shown in FIG. 19. Then, since, according to signal type information,count information, request information, and bit information input fromcontrol section 1601, retransmission has been requested for systematicbit data signal $1, systematic bit data signal $1 is read twice frommemory 1801 and systematic bit data signals $2 and $3 are read onceeach, and these signals are output to P/S conversion section 1604.

As shown in FIG. 19, the transmit signals output from S/P conversionsection 1603 are arranged in memory 1802 of P/S conversion section 1604in systematic bit data signal $1, $2, $1, $3 order from the top of FIG.19, then read sequentially from the top of FIG. 19, and converted toserial data format. The transmit signal output from P/S conversionsection 1604 is arranged as serial data format systematic bit datasequence “$1, $2, $1, $3” (ST2506).

If the transmit data is systematic bit data and the transmission is asecond retransmission, a transmit signal that has undergone spreadingprocessing by spreading section 1602 is converted from serial dataformat parity bit data sequence “$1, $2, $3, $4” to parallel data formatby S/P conversion section 1603, and stored temporarily in memory 1801,as shown in FIG. 20. Then, since, according to signal type information,count information, request information, and bit information input fromcontrol section 1601, this is a second retransmission and retransmissionhas been requested for systematic bit data signal $1, systematic bitdata signal $1 only is read four times from memory 1801 and output toP/S conversion section 1604.

As shown in FIG. 20, the transmit signals output from S/P conversionsection 1603 are arranged in memory 1802 of P/S conversion section 1604as systematic bit data signals $1, $1, $1, $1 from the top of FIG. 20,then read sequentially from the top of FIG. 20, and converted to serialdata format. The transmit signal output from P/S conversion section 1604is arranged as serial data format systematic bit data sequence “$1, $1,$1, $1” (ST2505).

The transmit signal then undergoes orthogonal frequency divisionmultiplexing processing such as IFFT processing by IFFT section 1605,and an OFDM-CDMA signal is obtained (ST2507).

The allocation of signals to subcarriers in an OFDM-CDMA signal obtainedin this way will now be described using FIG. 21 through FIG. 23.

When a transmit signal is parity bit data, or when a transmit signal issystematic bit data and transmission is normal (non-retransmission)transmission, as shown in FIG. 21 signal $1 is arranged distributedamong the subcarriers of first group G1, signal $2 is arrangeddistributed among the subcarriers of second group G2, signal $3 isarranged distributed among the subcarriers of third group G3, and signal$4 is arranged distributed among the subcarriers of fourth group G4.

When transmit data is systematic bit data and the transmission is afirst retransmission, as shown in FIG. 22 signal $1 is arrangeddistributed among the subcarriers of first group G1 and in third groupG3 signal $1 is arranged distributed among the subcarriers in the sameway as in first group G1, signal $2 is assigned to second group G2, andsignal $3 is assigned to fourth group G4. Therefore, in a firstretransmission, the number of subcarriers is doubled compared with anormal transmission by having signal $1 assigned to the subcarriers ofthird group G3.

When transmit data is systematic bit data and the transmission is asecond retransmission, as shown in FIG. 23 signal $1 is arrangeddistributed among the subcarriers of first group G1, and in second groupG2, third group G3, and fourth group G4, also, signal $1 is arrangeddistributed among the subcarriers in the same way as in first group G1.Therefore, in a second retransmission, the number of subcarriers isdoubled compared with a first retransmission by having signal $1assigned to the subcarriers of second group G2 and the subcarriers offourth group G4.

Thus, according to Embodiment 7, in addition to provision of the effectsof Embodiment 6 described above, turbo coding of transmit data isperformed by a turbo coding section that enables much better error ratecharacteristics to be obtained that with other error correction methods,enabling error rate characteristics to be significantly improved.

In this embodiment, the number of subcarriers to which parity bit datais assigned does not change, but this is not a limitation, and thenumber of subcarriers to which parity bit data is assigned may beincreased in accordance with the number of retransmissions. Also, inthis embodiment, in the case of a retransmission, the number ofsubcarriers to which systematic bit data is assigned and the number ofsubcarriers to which parity bit data is assigned are different, but thisis not a limitation, and the number of subcarriers to which systematicbit data is assigned and the number of subcarriers to which parity bitdata is assigned may be increased by the same number in accordance withthe number of retransmissions.

Embodiment 8

FIG. 26 is a block diagram showing the configuration of a transmittingapparatus 2600 according to Embodiment 8 of the present invention. Afeature of this embodiment is that a retransmission signal is assignedto subcarriers in accordance with channel quality information. Parts inFIG. 26 identical to those in FIG. 16 are assigned the same codes as inFIG. 16, and descriptions thereof are omitted.

Control section 1601 temporarily stores transmit signals modulated by amodulation section (not shown), and separates transmit signals intoretransmission information and normal information other thanretransmission information. Then, when transmission timing is reached,control section 1601 outputs a transmit signal to spreading section1602, and also outputs retransmission information to S/P conversionsection 1603 and P/S conversion section 1604. Control section 1601 alsofinds channel quality such as an SIR (signal to interference ratio) froma received signal, and outputs the found channel quality to S/Pconversion section 1603 and P/S conversion section 1604 as channelquality information. The method of finding channel quality from areceived signal can be employed in the case of a TDD (Time DivisionDuplex) communication method. Channel quality information may also bedetected and transmitted by a communicating party. In this case, signalto interference ratio channel quality information such as an SIRmeasurement result measured by the communicating party can simply betransmitted by the communicating party.

When retransmission information input from control section 1601indicates a normal transmission, not a retransmission, S/P conversionsection 1603 converts the transmit signal input from spreading section1602 directly from serial data format to parallel data format, andoutputs the resulting signal to P/S conversion section 1604. On theother hand, when retransmission information input from control section1601 indicates a retransmission, S/P conversion section 1603 generates anumber of data to be retransmitted included in retransmissioninformation in accordance with the number of retransmissions, convertsthe generated data from serial data format to parallel data format, andoutputs the converted data to P/S conversion section 1604. At this time,if it is determined from the channel quality information input fromcontrol section 1601 that channel quality is extremely poor, S/Pconversion section 1603 generates the number of retransmission signalsgenerated in the case of a second retransmission even if thetransmission is a first retransmission.

In a first transmission, P/S conversion section 1604 converts a transmitsignal input from S/P conversion section 1603 from parallel data formatto serial data format, and outputs this signal to IFFT section 1605. Ina retransmission, P/S conversion section 1604 performs rearrangement ofa transmit signal including retransmission data generated by S/Pconversion section 1603 according to retransmission information inputfrom control section 1601, and outputs the rearranged transmit signal toIFFT section 1605.

A turbo coding section 2601 outputs part of a transmit signal input fromcontrol section 1601 uncoded to a P/S conversion section 2602 assystematic bit data, and also performs recursive convolutional coding onthe remaining part of the input transmit signal and outputs this part toP/S conversion section 2602 as parity bit data.

P/S conversion section 2602 converts systematic bit data and parity bitdata input from turbo coding section 2601 from parallel data format toserial data format, and outputs these data to spreading section 1602.Systematic bit data and parity bit data are allocated to differentsymbols.

The operation of transmitting apparatus 2600 will now be described usingFIG. 18 through FIG. 20 and FIG. 27. FIG. 27 is a flowchart showing theoperation of transmitting apparatus 2600.

First, control section 1601 determines whether or not a transmit signalis a retransmission signal (ST2701), and in the case of a retransmissiondetermines whether or not this is the first retransmission (ST2702).Control section 1601 also determines whether or not channel quality isgood based on the channel quality found from the received signal. Anychannel quality determination method can be used, such as determiningwhether or not the channel quality is greater than or equal to athreshold value. Control section 1601 then outputs retransmissioninformation comprising signal type information, count information, andrequest information, and also channel quality information, to S/Pconversion section 1603 and P/S conversion section 1604.

In the case of normal (non-retransmission) transmission, a transmitsignal that has undergone spreading processing by spreading section 1602is converted from serial data format systematic bit data sequence “$1,$2, $3, $4” to parallel data format by S/P conversion section 1603, andstored temporarily in memory 1801, as shown in FIG. 18.

As the transmit signals output from S/P conversion section 1603 are in anormal transmission, they are not rearranged by P/S conversion section1604, and are arranged in memory 1802 in parity bit data signal $1, $2,$3, $4 order from the top of FIG. 18, then read sequentially from thetop of FIG. 18, and converted to serial data format. The transmit signaloutput from P/S conversion section 1604 is arranged as serial dataformat data sequence “$1, $2, $3, $4” (ST2703).

If the transmission is a first retransmission and channel quality isgood, a transmit signal that has undergone spreading processing byspreading section 1602 is converted from serial data format systematicbit data sequence “$1, $2, $3, $4” to parallel data format by S/Pconversion section 1603, and stored temporarily in memory 1801, as shownin FIG. 19. Then, since, according to signal type information, countinformation, request information, and channel quality information inputfrom control section 1601, this is a first retransmission,retransmission has been requested for signal $1, and channel quality isgood according to the result of determination of whether or not channelquality is good by control section 1601 (ST2705), signal $1 is readtwice from memory 1801 and signals $2 and $3 are read once each, andthese signals are output to P/S conversion section 1604.

As shown in FIG. 19, the transmit signals output from S/P conversionsection 1603 are arranged in memory 1802 of P/S conversion section 1604in signal $1, $2, $1, $3 order from the top of FIG. 19, then readsequentially from the top of FIG. 19, and converted to serial dataformat. The transmit signal output from P/S conversion section 1604 isarranged as serial data format data sequence “$1, $2, $1, $3” (ST2706).

On the other hand, if channel quality is poor even though thetransmission is a first retransmission, a transmit signal that hasundergone spreading processing by spreading section 1602 is convertedfrom serial data format systematic bit data sequence “$1, $2, $3, $4” toparallel data format by S/P conversion section 1603, and storedtemporarily in memory 1801, as shown in FIG. 20. Then, since, accordingto signal type information, count information, request information, andchannel quality information input from control section 1601, this is afirst retransmission, retransmission has been requested for signal $1,and channel quality is poor, signal $1 only is read four times frommemory 1801 and output to P/S conversion section 1604.

As shown in FIG. 20, the transmit signals output from S/P conversionsection 1603 are arranged in memory 1802 of P/S conversion section 1604in signal $1, $1, $1, $1 order from the top of FIG. 20, then readsequentially from the top of FIG. 20, and converted to serial dataformat. The transmit signal output from P/S conversion section 1604 isarranged as serial data format data sequence “$1, $1, $1, $1” (ST2704).

In the case of a second retransmission, a transmit signal that hasundergone spreading processing by spreading section 1602 is convertedfrom serial data format systematic bit data sequence “$1, $2, $3, $4” toparallel data format by S/P conversion section 1603, and storedtemporarily in memory 1801, as shown in FIG. 20. Then, since, accordingto signal type information, count information, and request informationinput from control section 1601, this is a second retransmission andretransmission has been requested for signal $1, signal $1 only is readfour times from memory 1801 and output to P/S conversion section 1604.

As shown in FIG. 20, the transmit signals output from S/P conversionsection 1603 are arranged in memory 1802 of P/S conversion section 1604in signal $1, $1, $1, $1 order from the top of FIG. 20, then readsequentially from the top of FIG. 20, and converted to serial dataformat. The transmit signal output from P/S conversion section 1604 isarranged as serial data format systematic bit data sequence “$1, $1, $1,$1” (ST2704).

The transmit signal then undergoes orthogonal frequency divisionmultiplexing processing such as IFFT processing by IFFT section 1605,and an OFDM-CDMA signal is obtained (ST2707).

The allocation of signals to subcarriers in an OFDM-CDMA signal obtainedin this way will now be described using FIG. 21 through FIG. 23.

In normal transmission in which a transmit signal is not aretransmission signal, as shown in FIG. 21 signal $1 is arrangeddistributed among the subcarriers of first group G1, signal $2 isarranged distributed among the subcarriers of second group G2, signal $3is arranged distributed among the subcarriers of third group G3, andsignal $4 is arranged distributed among the subcarriers of fourth groupG4.

When the transmission is a first retransmission and channel quality isgood, as shown in FIG. 22 signal $1 is arranged distributed among thesubcarriers of first group G1 and in third group G3 signal $1 isarranged distributed among the subcarriers in the same way as in firstgroup G1, signal $2 is assigned to second group G2, and signal $3 isassigned to fourth group G4. Therefore, in a first retransmission, thenumber of subcarriers is doubled compared with a normal transmission byhaving signal $1 assigned to the subcarriers of third group G3.

When the transmission is a second retransmission or a firstretransmission and channel quality is poor, as shown in FIG. 23 signal$1 is arranged distributed among the subcarriers of first group G1, andin second group G2, third group G3, and fourth group G4, also, signal $1is arranged distributed among the subcarriers in the same way as infirst group G1. Therefore, in a second retransmission, the number ofsubcarriers is doubled compared with a normal transmission by havingsignal $1 assigned to the subcarriers of second group G2 and thesubcarriers of fourth group G4.

Thus, according to Embodiment 8, in addition to provision of the effectsof Embodiment 6 described above, an S/P conversion section and P/Sconversion section arrange a retransmission signal so as to be assignedto subcarriers with channel quality also taken into consideration,enabling error rate characteristics to be improved dependably whenchannel quality is poor.

Embodiment 9

FIG. 28 is a drawing showing the configuration of a transmittingapparatus 2800 according to Embodiment 9 of the present invention. Afeature of this embodiment is that the number of subcarriers to which aretransmission signal is assigned is varied also taking the transmissiontime interval into consideration. In this embodiment, the configurationin FIG. 28 differs from that in FIG. 16 in including a counter section2801, a delay section 2802, a subtraction section 2803, and a sizecomparison section 2804. Parts in FIG. 28 identical to those in FIG. 16are assigned the same codes as in FIG. 16, and descriptions thereof areomitted.

When CSMA (Carrier Sense Multiple Access) is used as an access method,as in IEEE802.11, if a channel is congested the time interval betweenthe previous transmission and the present transmission may be very long.In such cases, transmission delay may be extremely long if there is anerror in a second or third retransmission. An effective method ofpreventing this problem is to vary the number of subcarriers to which aretransmission signal is assigned taking the transmission time intervalbetween the previous transmission and the present transmission intoconsideration. In CSMA, a terminal performs carrier sensing andtransmits if the reception level is less than or equal to a thresholdvalue.

Counter section 2801 generates information indicating transmissiontiming based on transmission timing input from control section 1601, andoutputs this generated information to delay section 2802 and subtractionsection 2803.

Delay section 2802 delays the information indicating transmission timinginput from counter section 2801, and outputs this information tosubtraction section 2803.

From the information indicating transmission timing input from countersection 2801 and the transmission timing input from delay section 2802,subtraction section 2803 calculates the difference between thetransmission timing of the previous transmission and the transmissiontiming of the present transmission, and outputs the calculatedtransmission timing difference to size comparison section 2804 as atransmission time interval.

Size comparison section 2804 compares the transmission time intervalinput from subtraction section 2803 with a threshold value, and outputstransmission time interval information as to whether or not thetransmission time interval is greater than or equal to the thresholdvalue to S/P conversion section 1603 and P/S conversion section 1604.

When the transmission is a normal transmission according toretransmission information input from control section 1601, S/Pconversion section 1603 converts a transmit signal input from spreadingsection 1602 directly from serial data format to parallel data format,and outputs the resulting signal to P/S conversion section 1604. On theother hand, when retransmission information input from control section1601 indicates a retransmission, S/P conversion section 1603 generates anumber of data to be retransmitted included in retransmissioninformation in accordance with the number of retransmissions, convertsthe generated data from serial data format to parallel data format, andoutputs the converted data to P/S conversion section 1604. At this time,if the length of the transmission time interval is greater than or equalto the threshold value according to the transmission time intervalinformation input from size comparison section 2804, S/P conversionsection 1603 generates retransmission signals equivalent to the numberof subcarriers used for retransmission signal assignment in the case ofa second retransmission even if the transmission is a firstretransmission.

In a first transmission, P/S conversion section 1604 converts a transmitsignal input from S/P conversion section 1603 from parallel data formatto serial data format, and outputs this signal to IFFT section 1605. Ina retransmission, P/S conversion section 1604 performs rearrangement ofa transmit signal including retransmission data generated by S/Pconversion section 1603 according to retransmission information inputfrom control section 1601, and outputs the rearranged transmit signal toIFFT section 1605.

The operation of transmitting apparatus 2800 will now be described usingFIG. 18 through FIG. 20 and FIG. 29. FIG. 29 is a flowchart showing theoperation of transmitting apparatus 2800.

First, control section 1601 determines whether or not a transmit signalis are transmission signal (ST2901) and if the transmit signal is aretransmission signal, determines whether or not this is the firstretransmission (ST2902). Also, subtraction section 2803 outputs thecalculated transmission time interval to S/P conversion section 1603 andP/S conversion section 1604.

In the case of a normal transmission—that is, a transmission that is nota retransmission—a transmit signal that has undergone spreadingprocessing by spreading section 1602 is converted from serial dataformat systematic bit data sequence “$1, $2, $3, $4” to parallel dataformat by S/P conversion section 1603, and stored temporarily in memory1801, as shown in FIG. 18.

As the transmit signals output from S/P conversion section 1603 are in anormal transmission, they are not rearranged by P/S conversion section1604, and are arranged in memory 1802 in signal $1, $2, $3, $4 orderfrom the top of FIG. 18, then read sequentially from the top of FIG. 18,and converted to serial data format. The transmit signal output from P/Sconversion section 1604 is arranged as serial data format data sequence“$1, $2, $3, $4” (ST2903).

In the case of a first retransmission, if the transmission time intervalinput from size comparison section 2804 is less than a threshold value,a transmit signal that has undergone spreading processing by spreadingsection 1602 is converted from serial data format systematic bit datasequence “$1, $2, $3, $4” to parallel data format by S/P conversionsection 1603, and stored temporarily in memory 1801, as shown in FIG.18. Then, since, based on signal type information, count information,request information, and transmission time interval information inputfrom control section 1601, this is a first retransmission according tothe result of determination of whether or not this is a firstretransmission by control section 1601 (ST2902), retransmission has beenrequested for signal $1, and the transmission time interval is less thanthe threshold value according to the result of determination of whetheror not the transmission time interval is greater than or equal to thethreshold value by size comparison section 2804 (ST2905), signal $1 isread twice from memory 1801 and signals $2 and $3 are read once each,and these signals are output to P/S conversion section 1604.

As shown in FIG. 19, the transmit signals output from S/P conversionsection 1603 are arranged in memory 1802 of P/S conversion section 1604in signal $1, $2, $1, $3 order from the top of FIG. 19, then readsequentially from the top of FIG. 19, and converted to serial dataformat. The transmit signal output from P/S conversion section 1604 isarranged as serial data format data sequence “$1, $2, $1, $3” (ST2906).

On the other hand, if the transmission is a first retransmission and thetransmission time interval input from size comparison section 2804 isgreater than or equal to the threshold value, a transmit signal that hasundergone spreading processing by spreading section 1602 is convertedfrom serial data format systematic bit data sequence “$1, $2, $3, $4” toparallel data format by S/P conversion section 1603, and storedtemporarily in memory 1801, as shown in FIG. 20. Then, since, accordingto signal type information, count information, request information, andtransmission time interval information input from control section 1601,this is a first retransmission, retransmission has been requested forsignal $1, and the transmission time interval is greater than or equalto the threshold value, signal $1 only is read four times from memory1801 and output to P/S conversion section 1604.

As shown in FIG. 20, the transmit signals output from S/P conversionsection 1603 are arranged in memory 1802 of P/S conversion section 1604in signal $1, $1, $1, $1 order from the top of FIG. 20, then readsequentially from the top of FIG. 20, and converted to serial dataformat. The transmit signal output from P/S conversion section 1604 isarranged as serial data format data sequence “$1, $1, $1, $1” (ST2904).

In the case of a second retransmission, a transmit signal that hasundergone spreading processing by spreading section 1602 is convertedfrom serial data format systematic bit data sequence “$1, $2, $3, $4” toparallel data format by S/P conversion section 1603, and storedtemporarily in memory 1801, as shown in FIG. 20. Then, since, accordingto signal type information, count information, and request informationinput from control section 1601, retransmission has been requested forsignal $1, signal $1 only is read four times from memory 1801 and outputto P/S conversion section 1604.

As shown in FIG. 20, the transmit signals output from S/P conversionsection 1603 are arranged in memory 1802 of P/S conversion section 1604in signal $1, $1, $1, $1 order from the top of FIG. 20, then readsequentially from the top of FIG. 20, and converted to serial dataformat. The transmit signal output from P/S conversion section 1604 isarranged as serial data format systematic bit data sequence “$1, $1, $1,$1” (ST2904).

The transmit signal then undergoes orthogonal frequency divisionmultiplexing processing such as IFFT processing by IFFT section 1605,and an OFDM-CDMA signal is obtained (ST2907).

The allocation of signals to subcarriers in an OFDM-CDMA signal obtainedin this way will now be described using FIG. 21 through FIG. 23.

In normal transmission in which a transmit signal is not aretransmission signal, as shown in FIG. 21 signal $1 is arrangeddistributed among the subcarriers of first group G1, signal $2 isarranged distributed among the subcarriers of second group G2, signal $3is arranged distributed among the subcarriers of third group G3, andsignal $4 is arranged distributed among the subcarriers of fourth groupG4.

When the transmission is a first retransmission and the transmissiontime interval is less than the threshold value, as shown in FIG. 22signal $1 is arranged distributed among the subcarriers of first groupG1 and in third group G3 signal $1 is arranged distributed among thesubcarriers in the same way as in first group G1, signal $2 is assignedto second group G2, and signal $3 is assigned to fourth group G4.Therefore, in a first retransmission, the number of subcarriers isdoubled compared with a normal transmission by having signal $1 assignedto the subcarriers of third group G3.

When the transmission is a second retransmission or a firstretransmission and channel quality is poor, as shown in FIG. 23 signal$1 is arranged distributed among the subcarriers of first group G1, andin second group G2, third group G3, and fourth group G4, also, signal $1is arranged distributed among the subcarriers in the same way as infirst group G1. Therefore, in a second retransmission, the number ofsubcarriers is doubled compared with a normal transmission by havingsignal $1 assigned to the subcarriers of second group G2 and thesubcarriers of fourth group G4.

Thus, according to Embodiment 9, in addition to provision of the effectsof Embodiment 6 described above, an S/P conversion section and P/Sconversion section arrange a retransmission signal so as to be assignedto subcarriers with the transmission time interval also taken intoconsideration, making it possible to prevent transmission delay frombecoming extremely long due to numerous retransmissions when thetransmission time interval is long.

Embodiment 10

FIG. 30 is a drawing showing the configuration of a transmittingapparatus 3000 according to Embodiment 10 of the present invention. Afeature of this embodiment is that the number of subcarriers to which aretransmission signal is assigned is varied also taking the used bandusage situation into consideration. Parts in FIG. 30 identical to thosein FIG. 16 are assigned the same codes as in FIG. 16, and descriptionsthereof are omitted.

If information on the band usage situation is reported from thecommunicating party, or the band whose use is permitted is known as ausable bandwidth, control section 1601 can ascertain how much of amargin there is in the remaining band by finding the ratio of the usedband currently being used to the band whose use is permitted, andtherefore outputs information on the ratio of the used band to the bandwhose use is permitted (hereinafter referred to as “band information”)to S/P conversion section 1603 and P/S conversion section 1604.

When retransmission information input from control section 1601indicates a normal transmission, S/P conversion section 1603 converts atransmit signal input from spreading section 1602 directly from serialdata format to parallel data format, and outputs the resulting signal toP/S conversion section 1604. On the other hand, when retransmissioninformation input from control section 1601 indicates a retransmission,S/P conversion section 1603 generates a number of data to beretransmitted included in retransmission information in accordance withthe number of retransmissions, converts the generated data from serialdata format to parallel data format, and outputs the converted data toP/S conversion section 1604. At this time, if there is a margin in theband according to the band information input from control section 1601,S/P conversion section 1603 generates retransmission signals equivalentto the number of subcarriers used for retransmission signal assignmentin the case of a second retransmission even if the transmission is afirst retransmission.

In a first transmission, P/S conversion section 1604 converts a transmitsignal input from S/P conversion section 1603 from parallel data formatto serial data format, and outputs this signal to IFFT section 1605. Ina retransmission, P/S conversion section 1604 performs rearrangement ofa transmit signal including retransmission data generated by S/Pconversion section 1603 according to retransmission information inputfrom control section 1601, and outputs the rearranged transmit signal toIFFT section 1605.

The operation of transmitting apparatus 3000 will now be described usingFIG. 18 through FIG. 20 and FIG. 31. FIG. 31 is a flowchart showing theoperation of transmitting apparatus 3000.

First, control section 1601 determines whether or not a transmit signalis a retransmission signal (ST3101), and if the transmit signal is aretransmission signal, determines whether or not this is the firstretransmission (ST3102). Control section 1601 also determines the sizeof the ratio of the used band to the band whose use is permitted(ST3105), and outputs the result of this determination to S/P conversionsection 1603 and P/S conversion section 1604 as band information.

In the case of a normal transmission—that is, a transmission that is nota retransmission—a transmit signal that has undergone spreadingprocessing by spreading section 1602 is converted from serial dataformat systematic bit data sequence “$1, $2, $3, $4” to parallel dataformat by S/P conversion section 1603, and stored temporarily in memory1801, as shown in FIG. 18.

As the transmit signals output from S/P conversion section 1603 are in anormal transmission, they are not rearranged by P/S conversion section1604, and are arranged in memory 1802 in signal $1, $2, $3, $4 orderfrom the top of FIG. 18, then read sequentially from the top of FIG. 18,and converted to serial data format. The transmit signal output from P/Sconversion section 1604 is arranged as serial data format data sequence“$1, $2, $3, $4” (ST3103).

When the transmission is a first retransmission and there is no marginin the band, a transmit signal that has undergone spreading processingby spreading section 1602 is converted from serial data formatsystematic bit data sequence “$1, $2, $3, $4” to parallel data format byS/P conversion section 1603, and stored temporarily in memory 1801, asshown in FIG. 19. Then, since, based on signal type information, countinformation, request information, and band information input fromcontrol section 1601, this is a first retransmission, retransmission hasbeen requested for signal $1, and there is no margin in the band, signal$1 is read twice from memory 1801 and signals $2 and $3 are read onceeach, and these signals are output to P/S conversion section 1604.

As shown in FIG. 19, the transmit signals output from S/P conversionsection 1603 are arranged in memory 1802 of P/S conversion section 1604in signal $1, $2, $1, $3 order from the top of FIG. 19, then readsequentially from the top of FIG. 19, and converted to serial dataformat. The transmit signal output from P/S conversion section 1604 isarranged as serial data format data sequence “$1, $2, $1, $3” (ST3106).

If the transmission is a first retransmission and there is margin in theband, a transmit signal that has undergone spreading processing byspreading section 1602 is converted from serial data format systematicbit data sequence “$1, $2, $3, $4” to parallel data format by S/Pconversion section 1603, and stored temporarily in memory 1801, as shownin FIG. 20. Then, since, according to signal type information, countinformation, request information, and band information input fromcontrol section 1601, this is a first retransmission, retransmission hasbeen requested for signal $1, and there is margin in the band, signal $1only is read four times from memory 1801 and output to P/S conversionsection 1604.

As shown in FIG. 20, the transmit signals output from S/P conversionsection 1603 are arranged in memory 1802 of P/S conversion section 1604in signal $1, $1, $1, $1 order from the top of FIG. 20, then readsequentially from the top of FIG. 20, and converted to serial dataformat. The transmit signal output from P/S conversion section 1604 isarranged as serial data format data sequence “$1, $1, $1, $1” (ST3104).

In the case of a second retransmission, a transmit signal that hasundergone spreading processing by spreading section 1602 is convertedfrom serial data format systematic bit data sequence “$1, $2, $3, $4” toparallel data format by S/P conversion section 1603, and storedtemporarily in memory 1801, as shown in FIG. 18. Then, since, accordingto signal type information, count information, and request informationinput from control section 1601, this is a second retransmission andretransmission has been requested for signal $1, signal $1 only is readfour times from memory 1801 and output to P/S conversion section 1604.

As shown in FIG. 20, the transmit signals output from S/P conversionsection 1603 are arranged in memory 1802 of P/S conversion section 1604in signal $1, $1, $1, $1 order from the top of FIG. 20, then readsequentially from the top of FIG. 20, and converted to serial dataformat. The transmit signal output from P/S conversion section 1604 isarranged as serial data format systematic bit data sequence “$1, $1, $1,$1” (ST3104).

The transmit signal then undergoes orthogonal frequency divisionmultiplexing processing such as IFFT processing by IFFT section 1605,and an OFDM-CDMA signal is obtained (ST3107).

The allocation of signals to subcarriers in an OFDM-CDMA signal obtainedin this way will now be described using FIG. 21 through FIG. 23.

In normal transmission in which a transmit signal is not aretransmission signal, as shown in FIG. 21 signal $1 is arrangeddistributed among the subcarriers of first group G1, signal $2 isarranged distributed among the subcarriers of second group G2, signal $3is arranged distributed among the subcarriers of third group G3, andsignal $4 is arranged distributed among the subcarriers of fourth groupG4.

When the transmission is a first retransmission and there is no marginin the band, as shown in FIG. 22 signal $1 is arranged distributed amongthe subcarriers of first group G1 and in third group G3 signal $1 isarranged distributed among the subcarriers in the same way as in firstgroup G1, signal $2 is assigned to second group G2, and signal $3 isassigned to fourth group G4. Therefore, in a first retransmission, thenumber of subcarriers is doubled compared with a normal transmission byhaving signal $1 assigned to the subcarriers of third group G3.

When the transmission is a second retransmission or a firstretransmission and there is margin in the band, as shown in FIG. 23signal $1 is arranged distributed among the subcarriers of first groupG1, and in second group G2, third group G3, and fourth group G4, also,signal $1 is arranged distributed among the subcarriers in the same wayas in first group G1. Therefore, in a second retransmission, the numberof subcarriers is doubled compared with a normal transmission by havingsignal $1 assigned to the subcarriers of second group G2 and thesubcarriers of fourth group G4.

Thus, according to Embodiment 10, in addition to provision of theeffects of Embodiment 6 described above, an S/P conversion section andP/S conversion section arrange a retransmission signal so as to beassigned to subcarriers also taking into consideration whether or notthere is margin in the band, making it possible to prevent transmissiondelay from becoming long without lowering transmission efficiency whenthere is margin in the band.

Embodiment 11

FIG. 32 is a drawing showing the configuration of a transmittingapparatus 3200 according to Embodiment 11 of the present invention. Afeature of this embodiment is that an upper limit is set for the numberof retransmissions. In this embodiment, the configuration in FIG. 32differs from that in FIG. 16 in including a turbo coding section 3201, aselection section 3203, and a size comparison section 3204. Parts inFIG. 32 identical to those in FIG. 16 are assigned the same codes as inFIG. 16, and descriptions thereof are omitted.

Control section 1601, which is a retransmission count control section,temporarily stores transmit signals modulated by a modulation section(not shown) and separates transmit signals into retransmissioninformation and normal information other than retransmissioninformation. Then, when transmission timing is reached, control section1601 outputs a transmit signal to spreading section 1602, and alsooutputs retransmission information to S/P conversion section 1603, P/Sconversion section 1604, and size comparison section 3204. Controlsection 1601 also finds channel quality such as an SIR (signal tointerference ratio) from a received signal, and outputs the foundchannel quality to S/P conversion section 1603 and P/S conversionsection 1604 as channel quality information. Control section 1601 alsooutputs band information to selection section 3203. In addition, when asignal that aborts retransmission (hereinafter referred to as “abortsignal”) is input from size comparison section 3204, control section1601 halts retransmission signal output.

Turbo coding section 3201 outputs part of a transmit signal input fromcontrol section 1601 uncoded to P/S conversion section 3202 assystematic bit data, and also performs recursive convolutional coding onthe remaining part of the input transmit signal and outputs this part toP/S conversion section 3202 as parity bit data.

P/S conversion section 3202 converts systematic bit data and parity bitdata input from turbo coding section 3201 from parallel data format toserial data format, and outputs these data to spreading section 1602.Systematic bit data and parity bit data converted by P/S conversionsection 3202 is made up of all systematic bits or parity bits on asymbol-by-symbol basis.

Based on band information input from control section 1601, selectionsection 3203 selects a threshold value α or threshold value β andoutputs the selected threshold value to size comparison section 3204.That is to say, if the ratio of the present used band to the band whoseuse is permitted is large, threshold value β (where threshold valueα>threshold value β) is selected, and if the ratio of the present usedband to the band whose use is permitted is small, threshold value α isselected. As the threshold value is selected in accordance with bandinformation in this way, the upper limit of the number ofretransmissions can be varied adaptively according to the band usagesituation, and compatibility between overall system throughput and errorrate characteristics can be achieved.

Size comparison section 3204 compares the retransmission count based oncount information input from control section 1601 with threshold value αor threshold value β input from selection section 3203, and if theretransmission count is greater than or equal to the threshold value,outputs an abort signal to control section 1601. On the other hand, ifthe retransmission count is less than the threshold value, nothing isoutput. Except for aborting retransmission, the operation oftransmitting apparatus 3200 when the retransmission count reaches apredetermined number according to band information is identical to thatshown in FIG. 27, and therefore a description thereof is omitted here.

Thus, according to Embodiment 11, in addition to provision of theeffects of Embodiment 6, Embodiment 7, and Embodiment 8 described above,a size comparison section aborts retransmission when the retransmissioncount is greater than or equal to a threshold value, enabling overallsystem throughput to be increased.

In this embodiment it is assumed that threshold values selectedaccording to whether or not there is a margin in the band are of twokinds, threshold value α and threshold value β, but this is not alimitation, and selection may be made from among three or more thresholdvalues. Also, in this embodiment it is assumed that a transmit signal isturbo coded, but this is not a limitation, and a transmit signal may becoded by means of a coding method other than turbo coding. Furthermore,in this embodiment transmit signal rearrangement is performed also usingchannel quality information, but this is not a limitation, and transmitsignals may be rearranged using only retransmission information. Inaddition, in this embodiment it is assumed that a selection sectionselects a threshold value in accordance with the ratio of the used bandto the band whose use is permitted, but this is not a limitation, andany method may be employed, such as selecting a threshold value basedsimply on the size of the used band.

In Embodiment 1 through Embodiment 5 above a case has been described inwhich the number of retransmissions is two, but the number ofretransmissions is not limited to two, and the number of retransmissionscan be made any number.

Also, in Embodiment 1 through Embodiment 5 above it is assumed thatthree kinds of GI length are set, but these embodiments are not limitedto the case where three kinds of GI length are set, and it is possibleto set GI lengths of any kind.

Moreover, in Embodiment 1 through Embodiment 5 above it is assumed thatthe GI length is set to one-eighth, one-fourth, or three-eighths of theeffective symbol length according to the number of retransmissions, butthis is not a limitation, and it is possible to set any length as the GIlength according to the number of retransmissions.

Furthermore, in Embodiment 1 through Embodiment 5 above it is assumedthat all subcarriers are divided into four groups, but this is not alimitation, and it is possible to use any subcarrier arrangement.

In addition, in Embodiment 6 through Embodiment 11 above it is assumedthat the number of subcarriers to which signals are assigned from anormal transmission to a second transmission is changed, but this is nota limitation, and the number of subcarriers to which retransmissionsignals are assigned may be increased from a normal transmission to athird transmission.

In Embodiment 6 through Embodiment 11 above it is assumed thatincreasing the number of assigned subcarriers from a normal transmissionto a second retransmission is carried out on a group-by-group basis, butthis is not a limitation, and in the case of an OFDM signal, the numberof assigned subcarriers may be increased from a normal transmission to asecond retransmission on a subcarrier-by-subcarrier basis, withoutgrouping subcarriers.

Also, in Embodiment 6 through Embodiment 11 above it is assumed that aretransmission signal is read a plurality of times from an S/Pconversion section, and the number of subcarriers to which aretransmission signal is allocated is increased by performing transmitsignal rearrangement by means of a P/S conversion section 1604, but thisis not a limitation, and the number of subcarriers to which aretransmission signal is allocated may be increased when orthogonalfrequency division multiplexing processing is performed by an IFFTsection without performing rearrangement, or the number of subcarriersto which a retransmission signal is allocated may be increased byproviding separately an IFFT section that performs orthogonal frequencydivision multiplexing processing of a retransmission signal and an IFFTsection that performs orthogonal frequency division multiplexingprocessing of a normal signal.

Moreover, in Embodiment 6 through Embodiment 11 above it is assumed thatsubcarriers are divided into four groups, but this is not a limitation,and any number of groups can be used.

Furthermore, in Embodiment 6 through Embodiment 11 above it is assumedthat retransmission signals are newly generated by an S/P conversionsection, but this is not a limitation, and a transmit signal may betemporarily stored in memory and a retransmission signal read frommemory a number of times in accordance with the number ofretransmissions.

A transmitting apparatus described in Embodiment 1 through Embodiment 11above can be applied to a base station apparatus or a communicationterminal apparatus.

As described above, according to the present invention it is possible toprevent an increase in transmission delay due to an excessive increasein the number of retransmissions with almost no lowering of transmissionefficiency.

This application is based on Japanese Patent Application No. 2002-333448filed on Nov. 18, 2002, and Japanese Patent Application No. 2002-355079filed on Dec. 6, 2002, the entire content of which is expresslyincorporated by reference herein.

INDUSTRIAL APPLICABILITY

The present invention is suitable for use in a transmitting apparatusand transmitting method that use a multicarrier modulation method suchas OFDM (Orthogonal Frequency Division Multiplexing).

1. A transmitting apparatus comprising: a coding section that encodes atransmit signal and outputs systematic bit data and parity bit data; aspreading section that performs spreading processing of the systematicbit data and the parity bit data, with a spreading ratio of “1”; amultiplexing section that code-multiplexes the systematic bit data andthe parity bit data subjected to spreading processing in said spreadingsection, with a code multiplexing number of “1”; an insertion sectionthat inserts a first guard interval in the systematic bit datacode-multiplexed in said multiplexing section and inserts a second guardinterval in the parity hit data code-multiplexed in said multiplexingsection; and a control section that sets a length of the first guardinterval longer than a length of the second guard interval and lengthensthe length of the first guard interval in accordance with an increase ina number of retransmissions of the systematic bit data and the paritybit data.
 2. The transmitting apparatus according to claim 1, furthercomprising an allocation section that allocates the systematic bit dataand the parity bit data to different symbols.
 3. The transmittingapparatus according to claim 1, wherein said control section sets thelength of the first guard interval and the length of the second guardinterval according to delay distribution information.
 4. Thetransmitting apparatus according to claim 3, wherein said delaydistribution information is transmitted from a communicating party. 5.The transmitting apparatus according to claim 3, further comprising adetection section that detects said delay distribution information froma received signal.
 6. The transmitting apparatus according to claim 1,wherein said control section sets the length of the first guard intervaland the length of the second guard interval according to a transmissiontime interval.
 7. The transmitting apparatus according to claim 1,wherein said control section sets the length of the first guard intervaland the length of the second guard interval according to a used band. 8.The transmitting apparatus according to claim 7, wherein said controlsection makes the length of the first guard interval and the length ofthe second guard interval longer proportion as a ratio of said used bandto a band whose use is permitted is smaller.
 9. The transmittingapparatus according to claim 1, wherein said control section makes alength of the first guard interval and a length of the second guardinterval upon retransmission of the systematic bit data and the paritybit data, an integral multiple of a length of the first guard intervaland a length of the second guard interval upon first transmission of thesystematic bit data and the parity bit data.
 10. A base stationapparatus comprising a transmitting apparatus according to claim
 1. 11.A communication terminal apparatus comprising a transmitting apparatusaccording to claim
 1. 12. A guard interval setting method comprising: astep of encoding a transmit signal and outputting systematic bit dataand parity bit data; a step of performing spreading processing of thesystematic bit data and the and bit data outputted, using a spreader,with a spreading ratio of “1”; a step of code-multiplexing thesystematic bit data and the pant bit data subjected to spreadingprocessing, using a multiplexer, with a code multiplexing number of “1”;a step of inserting a first guard interval in the code-multiplexedsystematic bit data and inserting a second guard interval in thecode-multiplexed parity bit data; and a step of setting a length of thefirst guard interval longer than a length of the second guard intervaland lengthening the length of the first guard interval, in a controlsection, in accordance with an increase in a number of retransmissionsof the systematic bit data and the parity bit data.